Hypothesis: The authors cited previous data from their laboratory indicating that consumption of a carbohydrate and protein solution immediately after prolonged exercise prevented the decrease in bacterially-stimulated neutrophil degranulation that normally occurs. Given that neutrophil degranulation is an important factor in immune system defenses, preventing the decrease in neutrophil degranulation is considered to be a positive change. The authors could not tell if their previous findings were related specifically to the combination of carbohydrate and protein or if carbohydrate feeding alone would be sufficient, so they tested the effect of postexercise carbohydrate feeding alone versus carbohydrate and protein on bacterially-stimulated neutrophil degranulation.

Subjects: The subjects were 12 healthy male competitive endurance runners (mean age = 29 y, mean body mass 77 kg). They were nonsmokers and refrained from caffeine and alcohol for 72 h before the test and exercise for 24 h before the test.

Protocol:The subjects were fed a standardized diet for 24-h prior to the testing session. On the day of each test, subjects ate a standardized body mass and urine specific gravity (to assure normal hydration status) were measured and blood and saliva samples were collected for measurement of leukocytes, lymphocytes, neutrophils, elastase (marker of neutrophil degranulation), insulin, glucose, and cortisol. Subjects then exercised for 2 h at a previously determined treadmill speed that elicited 75% of VO2 max. Postexercise body mass was measured and blood and saliva samples were again obtained. The recovery beverages were consumed and further blood/saliva samples were collected at 30-min intervals for 3 hours after the exercise completion.

Summary of research findings

There were no time x trial interactions for circulating leukocyte, neutrophil, or lymphocyte counts or for the neutrophil:lymphocyte ratio (i.e., no treatment effect). However, there was a main effect for time for all of the above parameters. Both leukocyte and neutrophil counts were elevated by the bout of exercise (even after correction for change in plasma volume) and remained elevated compared with the pre-exercise value for the full 3 hours of recovery.

Both the carbohydrate and carbohydrate-protein treatments increased plasma elastase levels relative to placebo. There were no significant differences between the carbohydrate and carbohydrate-protein treatments, though. The differences persisted for nearly the entire 3-hour recovery period.

Plasma glucose higher for both the carbohydrate and carbohydrate-protein treatments versus the placebo at 30-150 min of recovery. There were no differences between carbohydrate and carbohydrate-protein, however. Both treatments also increased insulin relative to placebo, with somewhat larger insulin responses observed with the carbohydrate-protein treatment.

There were no differences among treatments in plasma cortisol, which peaked at 30 min postexercise for each treatment.

Interpretation of findings/Key practice applications

This study replicated this group’s earlier findings that a carbohydrate-protein postexercise feeding can attenuate the decrease in bacterially-stimulated postexercise neutrophil degranulation. However, this study extends this knowledge by showing that protein, at the level fed, offers no additional benefits compared with the same amount of carbohydrate alone. Neutrophil degranulation was used as a marker of an improve immune response in this study, but it is not clear what the actual physiological significance of this change was regarding the actual protection against illness in athletes.